Abstract: Static Frequency Converter (SFC) is widely used in the transport industry, power industry, industrial automation, and new energy industry and has become an important part of modern industrial production. However, SFC-driven motors are prone to power quality problems. For example, in pumped storage power plants, harmonics generated by SFC start to cause damage to power plant equipment or malfunction of automatic devices, and even harmonics are transmitted to the higher-level grid, affecting the safe and stable operation of the grid. Because of the harmonic problems during SFC starting, the mechanism of non-characteristic harmonic generation is investigated, an accurate mathematical model of the SFC grid-side current is established considering the current-limiting choke, and the main factors affecting the content of non-characteristic harmonics are analyzed to reveal the universal influence of the intermittent commutation process, the internal disturbance of the motor and the external disturbance process on the non-characteristic harmonic law. Finally, a Matlab/Simulink simulation model is constructed based on the actual parameters of a pumped storage power plant, which is combined with the field test results to verify the correctness and accuracy of this paper's analysis of the non-characteristic harmonic characteristics of the pumped storage power plant.